The chief use of iodine is for its antiseptic property. It is bactericidal, sporicidal, protozoacidal, cysticidal, and virucidal. Liquid formulations of iodine are usually prepared in ethanol (tincture of iodine) to increase solubility and concentration. Lugol solution is 5% iodine and 10% iodide in water. Iodoform is triiodomethane (CHI3). Iodophors such as povidone-iodine (Betadine) consist of iodine linked to a large-molecular-weight molecule. These are usually less toxic owing to the slow release of iodine from the carrier molecule. Radioactive iodine is used in the treatment of thyroid cancer. The antiarrhythmic drug amiodarone releases iodine and may cause either thyrotoxicosis or hypothyroidism after prolonged use. Iodine also is used in the manufacture of dyes and photographic reagents. Table salt is fortified with iodine.
Mechanism of toxicity. Toxicity can occur through skin absorption, ingestion, or inhalation. When ingested, iodine can cause severe corrosive injury to the GI tract owing to its oxidative properties. In the body, iodine is converted rapidly to iodide and stored in the thyroid gland.
The toxic dose depends on the product and the route of exposure. Iodophors and iodoform are generally less toxic, as iodine is released more slowly. However, significant systemic absorption has occurred in patients receiving povidone-iodine treatment on areas of skin breakdown.
Iodine vapor. The ACGIH-recommended workplace ceiling limit (TLV-C) for iodine vapor is 0.1 ppm (1 mg/m3). The air level considered immediately dangerous to life or health (IDLH) is 2 ppm.
Skin and mucous membranes. Strong iodine tincture (7% iodine and 5% potassium iodide in 83% ethanol) may cause burns, but USP iodine tincture (2% iodine and 2% sodium iodide in 50% ethanol) is not likely to produce corrosive damage. Systemic absorption of iodine may occur after an acute application of strong iodine tincture or after chronic applications of less concentrated products.
Ingestion. Reported fatal doses vary from 200 mg to more than 20 g of iodine; an estimated mean lethal dose is approximately 2–4 g of free iodine. USP iodine tincture contains 100 mg of iodine per 5 mL, and strong iodine tincture contains 350 mg of iodine per 5 mL. Iodine ointment contains 4% iodine. Consider ethanol toxicity with large exposures (See Ethanol).
Clinical presentation. The manifestations of acute iodine ingestion are related largely to the corrosive effect on mucous membranes and the GI tract.
Inhalation of iodine vapor can cause severe pulmonary irritation, which can lead to pulmonary edema.
Skin and eye exposures may result in severe corrosive burns.
Ingestion can cause corrosive gastroenteritis with vomiting, hematemesis, and diarrhea, which can result in significant volume loss and circulatory collapse. Pharyngeal swelling and glottic edema have been reported. Mucous membranes are usually stained brown, and the vomitus may be blue if starchy foods are already present in the stomach.
Chronic ingestions or absorption may result in hypothyroidism and goiter, or hyperthyroidism. Iodides cross the placenta, and neonatal hypothyroidism and death from respiratory distress secondary to goiter have been reported.
Chronic iodine ...